Then by my personal standards it would be entirely appropriate for that particular piece of paper to be used as a tipped in signature (I also have a facsimilie of the note that you linked to -- booksellers seem to like providing it as a bookmark). However, the vast majority of tipped in signatures were not intended for that purpose, and indeed the one in question doesn't appear to have been intended for that.

As always, the owner is entitled to do whatever they want with it, it just isn't what I would do, and seems [to me] to be pointless to make two original things less original by sticking them together.

That the market apparently values the two items glued together more highly than the two items in their original form seems like a type of madness.